1. Field of the Invention
The present invention relates to loudspeakers and more particularly to dual spider arrangements for use in combination with the loudspeakers.
2. Description of the Prior Art
U.S. Pat. No. 2,812,825, entitled Loud Speaker Diaphragm Supporting Member, issued Charles L. Matthews on Nov. 12, 1957, teaches a member for supporting a moving coil in an electro-acoustical transducer and for centering such coil in an air gap in such transducer. The member includes a corrugated disc of resin-impregnated, thin, resilient, porous cotton fabric and an external film of modified polyvinyl chloride type resin on the surface of the disc to fill the pores in the cotton.
U.S. Pat. No. 2,641,329, entitled Loudspeaker Diaphragm with Transversely Arched Stiffener Means, issued to Sidney E. Levy and Abraham B. Cohen on June 9, 1953 teaches an acoustic diaphragm for loudspeakers, that include an acoustical energy-responsive diaphragm member of substantially conical form having a relatively rigid transversely arched stiffener member secured at its outer marginal edge to an intermediate portion of the diaphragm member and extending across the latter. The stiffener member has a plurality of relatively small sound-radiating perforations therethrough, the perforations of the stiffener member being spaced from each other and each perforation having its axis inclined at an angle to the central axis of the diaphragm member. The perforated stiffener member has the property of directional control of high frequency propagation generated from the center of the diaphragm member.
U.S. Pat. No. 3,905,448, entitled Loudspeaker, issued to Hirotake Kawakami, Toshio Sasabe, Toshio Hirosawa, Nobuyaki Arakawa, Kozo Kokubu, Kazumasa Abe and Toshiko Harashino, on Sept. 16, 1975 teaches a loudspeaker with a suspension device for supporting the diaphragm from its frame. In the loudspeaker, the upper part and the lower part of a cone-shaped diaphragm with a voice coil are suspended from a frame by a ring-shaped suspension member, herein referred to as a first suspension means, and by a ring-shaped suspension member, herein referred to as a suspension means, respectively. At least one of the suspension means is formed of a mixture of elastic material such as rubber, with carbon fibers therein. The fibers are needle-like and are aligned radially in the material of at least one of the suspension means.
U.S. Pat. No. 3,767,004, entitled loudspeaker, issued to Arthur Liebscher on Oct. 23, 1973, teaches a loudspeaker that is provided in which a thin surround is employed for the speaker cone of impervious foam material, the surround being characterized by omni-directional elastic tension and being secured between the cone and the support.
The loudspeaker also has a pair of spaced coaxial supports which support the coil. The supports have radial rigidity and high axial flexibility so that the surround serves no supporting function and acts primarily as an air separator at the periphery of the diaphragm.
Abraham B. Cohen has written an article entitled, The Mechanics of Good Loudspeaker Design, published in Volume 2, Number 3, July, 1954, Journal of the Audio Engineering Society on pages 176 to 182. In his article he discusses a double spider to correct voice coil misalignment as follows:
"Having thus dealt briefly with one of the unrecognized causes of gap and voice coil misalignment, we must complete the study of the problem by considering the more commonly recognized cause of such misalignment. Damaging eccentric and rocking motion of the voice coil about its axis of motion will occur while it is vibrating, if the means used to maintain accuracy of such motion are inadequate to meet the mechanical requirements imposed on the system by the large power output expected of it. The usual means for preventing such side swaying of the voice coil motion is the well-known spider located directly at the voice coil area. There is a new and exceedingly successful solution to the problem of maintaining precision voice coil alignment during vibration. Placement of two axially spaced spiders at the apex area of the vibrating system provides a dual guide to the vibrating system that keeps the voice coil motion rigidly channeled along one line of vibration that neither deviates in angular direction from the central axis nor becomes eccentrically located in respect to this axis."
In his book, Hi-Fi Loudspeakers and Enclosures, 2nd Edition, Abraham B. Cohen further describes a dual spider arrangement on pages 87 to 88 in which he states:
"The mechanical precision with which the suspension holds the whole assembly together determines the mechanical longevity of the voice coil itself. The voice coil must be kept perfectly aligned mechanically in its magnetic gap at all times during its vibration cycle. If, during its vibration, it sways or twists sideways, it may scrape itself against the walls of the gap, causing rubbing of the voice coil, which in turn results in distortion, in shorted turns, and sooner or later, in an open voice coil. Although the spider is normally the device that keeps the coil centered in the gap when no motion is involved it is the combination of the spider and the other cone suspension that dictates how the coil behaves in the gap under motion. Obviously, even though the spider may keep the coil centered, if the cone tilts, it will tilt the coil and cause rubbing. Where small motions are involved, as in tweeters, this condition does not present a problem. However, in the case of woofers, where voice coil motions of the order of 3/8 inch or more are prevalent, added insurance against voice coil misalignment may be had by the double spider suspension. The addition of the second stabilizing spider part way up the cone of the speaker acts as a second guide to the linear in and out motion of the voice coil, keeping the voice coil not only rigidly centered, but also moving in a rigidly prescribed axis."
"In loudspeakers in which the voice coil travels a straight and narrow path, and in which the side play of the coil is rigidly controlled, the clearances between the overall gap walls and the voice coil may be reduced, with resultant improved magnetic circuit efficiency, because of the reduced gap cross-section. thus we see again that the final acoustic performance of the loudspeaker is a function of the mechanical tolerances permissible between controlled moving parts."
There have been several other loudspeakers that have incorporated dual spiders for supporting their diaphragms. the difficulty with these dual spiders is that their manufacturer is unable to adjust the linearity of the loudspeakers' response after manufacture thereof. The two externally placed spiders are disposed in a fixed position. It would be ideal to provide an adjustable spider for loudspeakers that can reduce the bias in the response thereof.